The present invention relates to radiography imaging systems, and more particularly to an interdigital structure for a photoconductive detector in a radiography imaging system.
Traditionally, medical diagnostic processes record x-ray image patterns on silver halide films. These systems direct an initially uniform pattern of interrogating x-ray radiation through a patient to be studied, intercept the consequently imagewise modulated pattern of x-ray radiation with an x-ray radiation intensifying screen, record the intensified pattern in a silver halide film, and chemically transform the latent radiation pattern into a permanent and visible image called a radiogram.
Radiograms have also been produced by using layers of radiation sensitive materials to directly capture radiographic images as imagewise modulated patterns of electrical charges. Depending upon the intensity of the incident X-ray radiation, electrical charges generated either electrically or optically by the X-ray radiation within a pixelized area are quantized using a regularly arranged array of discrete solid state radiation sensors.
There has been rapid development of large area, flat panel, digital x-ray imaging detectors for digital radiology using active matrix technologies. An active matrix consists of a two-dimensional array of thin film transistors (TFTs) made with amorphous or polycrystalline semiconductor materials. There are two general approaches to making flat-panel x-ray detectors, direct or indirect. The direct method is also referred to as a self-scanned xcex1-Se (amorphous selenium). The indirect method uses phosphor screens or other scintillators, e.g., cesium iodide (CsI), to first convert x-rays to visible light, which is then read out with an active matrix array with an additional light sensor, i.e., a photodiode, at each pixel of the array.
While achieving advantages over traditional film radiography, photodiode use in x-ray imaging has its share of difficulties. In the indirect method, the use of photodiodes presents size limitations, complex design and therefore high cost. The minimal pixel size for developed photodiode flat panel is about 125 micron by 125 micron. Unfortunately, the size limitations restrict the resolution of the array. Accordingly, a need exists for a photodetector structure that reduces these problems in a flat-panel radiographic detector.
The present invention meets this need and provides system and method aspects for a photoconductive element for a radiography imaging system. The photoconductive element includes a conducting layer for absorbing photons generated indirectly from radiation passing through an object being imaged by the radiography imaging system. Also included is an interdigital contact structure in the conducting layer.
The interdigital contact structure for electrodes in accordance with the present invention reduces the gap between electrodes, which results in a negligible photoconductive lag. Also, a small electrode gap supports an increase in the gain of the detector, since the gain is inversely proportional to the distance between the electrodes. Further, the interdigital structure of the present invention is simpler and correspondingly less expensive in comparison to a traditional photodiode structure. These and other advantages of the aspects of the present invention will be more fully understood in conjunction with following detailed description and accompanying drawings.